Linear arrays of miniature light modulators form the basis for a broad family of MEMS-based video displays. These displays form line images that are swept back and forth to “paint” two-dimensional scenes. FIGS. 1A-1C show display system concepts for a linear array MEMS display.
In FIGS. 1A-1C, light source 105 illuminates MEMS linear array 115 through lens 110. Array 115 is shown schematically, and enlarged, in inset 120. Elements 116, 117 and 118 are just a few of the light modulator elements that form the array. Array 115 may operate in transmission or reflection. For example, one type of linear array light modulator is formed from thousands of reflective micro-electromechanical ribbons arranged in a single column.
Array 115 imparts phase information onto a narrow strip of light. Optical system 125 then converts the phase information into amplitude variations to form a line image. Scan mirror 130 scans a line image 135 across a screen such as screen 140 shown in FIG. 1B. The line image is scanned fast enough that the scanning motion is not noticeable to the human eye. Scanned line images on screen 140 provide a full video experience.
Optical system 125 may take different forms which are complementary to different methods of encoding phase information with array 115. Some examples of such optical systems are presented in U.S. Pat. No. 7,054,051 (“Differential interferometric light modulator and image display device”), U.S. Pat. No. 7,286,277 (“Polarization light modulator”) and U.S. Pat. No. 7,940,448 (“Display system”).
One of the properties of MEMS light modulators which enables their use in linear array display systems like that of FIGS. 1A-1C is their high speed. The two-dimensional image formed on screen 140 is updated many times per second, and each two-dimensional image is formed by successive line images, each different from the next. A change from one line image to another requires reconfiguring linear array elements. The time available to do this is called a “column time”. High resolution video displays put extreme requirements on MEMS switching speed as the column time available is short.
Consider, for example, a “4K” video display having 4096 columns by 2160 rows of pixels. If the display operates at 196 frames per second, and is reconfigured to display red, green and blue information sequentially on a column by column basis, then the amount of time that the linear array remains in any particular configuration is only a few hundred nanoseconds.
As resolution requirements become even greater and the desired number of frames of video information per second also increases, the time available to reconfigure a linear array for each new column (i.e. each new line image) becomes a limiting factor. Of course, in the example above, one could turn the display chip on its side and use an array with 4096 elements to generate 2160 columns, but that strategy requires a display chip twice as long, using up valuable wafer real estate.
Hence, what are needed are linear-array MEMS display chips that can provide high-resolution, high-frame rate video.